A death row inmate who shot and killed a 61-year-old grandmother inside her home during an eight-day crime spree has been executed.

Mark Anthony Soliz, 37, received a lethal injection at the Texas state penitentiary in Huntsville for the June 2010 slaying of Nancy Weatherly during a robbery at her rural home near Godley.

During a five-minute final statement, Soliz apologised profusely to his victim's son and daughter-in-law, who watched through a window a few feet from him, telling them: "I don't know if me passing will bring y'all comfort for the pain and suffering I caused y’all.”

Soliz apologised profusely shortly before he was executed (Getty)

He added: "I am at peace. I understand the pain that I caused y’all."

He said he made wrong decisions but forgave himself and was "going with a humble heart”.

As the lethal dose of pentobarbital began, he again turned his head toward Weatherly's relatives, telling them: "I hope y'all forgive me.”

Eighteen minutes later - at 6.32pm - he was pronounced dead.

His victim's family members declined comment afterward.

Soliz victim Ruben Martinez pictured with his wife Lisa Martinez, who testified in the trial, and their young son (Getty)

State and federal appeals courts and the Texas Board of Pardons and Paroles turned down requests by Soliz's attorneys to stop the execution, after they argued that he suffered from foetal alcohol spectrum disorder, which left him with brain damage.

His attorneys said the disorder is the "functional equivalent" of conditions already recognised by the US Supreme Court as disqualifying exemptions to the death penalty, such as intellectual disability.

Prosecutors portrayed Soliz as a dangerous individual who killed Ms Weatherly for a "pittance of property”.

At his trial, prosecutors said Soliz and another man, Jose Ramos, committed at least 13 crimes in the Fort Worth area over eight days in June 2010.

The killer was killed by lethal injection after a five-minute final statement (Getty/stock pic)

After fatally shooting a deliveryman around 6am on June 29, 2010, the duo later that morning drove in a stolen car to Ms Weatherly's home.

Prosecutors say Soliz and Ramos forced their way into the home at gunpoint and ransacked the place, taking a television, mobile phones and credit cards.

Prosecutors say Ms Weatherly begged for her life and pleaded with Soliz not to take her deceased mother's jewellery box before she was shot in the back of the head.

Soliz was the 15th inmate put to death this year in the US and his was the sixth execution in Texas and the second in as many weeks in the state.

Nine more executions are scheduled this year in Texas, the busiest capital punishment state in the United States.